Diseases of the long bones, particularly in the extremities, often necessitate the implantation of a long-shafted endoprosthesis, which serves to strengthen the bone and which in many cases also serves at the same time for anchoring a joint element of a joint endoprosthesis, for example a knee prosthesis. Generally, the shaft is inserted into the bone, for example a femur, from the side where the pathological defect is situated. In the case of a knee-joint endoprosthesis, this means that the shaft is usually inserted from the knee end (distal end) of the femur. However, there are also special pathological cases in which the shaft is inserted from the opposite end (i.e., in the case of the knee-joint endoprosthesis, from the proximal end of the femur) and then pushed through the medullary cavity of the bone. Shafts of this kind are generally known by the name “through-going shaft”.
A case may arise in which there is also a disease located at the other end of the through-going shaft and requiring treatment with a prosthesis. Taking the example of the knee-joint endoprosthesis, this means that a disease occurs in the area of the hip joint and, consequently, the subsequent implantation of a hip-joint endoprosthesis may be indicated. In practice, this often means that the through-going shaft has to be exchanged. This is a difficult operation and often involves further loss of substance from a bone that is in any case already weakened by disease. Particularly difficult cases are ones in which fractures have already occurred in the damaged joint area (for example, in the case of the hip joint, a fracture of the neck of the femur), which may also result in different lengths of the extremities. This is a severe disadvantage to patients.